1. Field of the Invention
The field of the present invention pertains to circuitry to solve the problems caused by capacitive and inductive coupling in signals in an integrated circuit device. This particular issue of capacitive and inductive coupling in signals is becoming increasingly difficult as the industry advances and moves towards reduction in circuit device size (for example, from 0.25 uM technology to 0.18 uM, 0.15 uM, 0.13 uM and beyond).
2. Related Art
With their growth in commercial markets and consumer demands for smaller Integrated Circuits (ICs—which are used in numerous applications such as cellular phones, wristwatch cameras, and hand-held organizers just to name a few) increase, IC size requirement trends continue towards a small form factor and lowered power consumption. As these IC size requirements shrink, semiconductor manufacturers are forced to design circuits at a much smaller level than in the past. Previously, as the industry moved from Very Large Scale Integration (VLSI) to Ultra Large Scale Integration (ULSI), the relative capacitive and inductive coupling of the circuit itself was not realized to be as critical of an issue.
However, as the semiconductor industry designs and implements circuitry on sub-micron level technology (where spacing between circuitry lines is less than 10−6 m) and beyond, the capacitive and inductive coupling of the signal lines within the circuitry itself is realized to be a critical problem for designers. As circuit size becomes smaller and the relative distances for signal lines becomes longer, the problem of coupling and or cross talk between signal lines and ground or power lines becomes more evident. Furthermore, as the signal line to ground coupling and/or other signal lines becomes stronger, the signal to noise ratio for given signals increases proportionally. This particular issue of capacitive and inductive coupling in signals is becoming increasingly difficult as the industry advances and moves towards reduction in circuit device size (for example, from 0.25 uM technology to 0.18 uM, 0.15 uM, 0.13 uM and beyond).
One prior art approach to minimize the signal to noise ratio (or capacitive and inductive coupling), is to strengthen the signal drive level. By increasing the signal strength, the total signal to noise ratio is reduced. Unfortunately, to increase the signal strength, the device must also be supplied higher power. This solution is inconsistent with the modern trend of reducing power consumption in ICs for heat issues, portability issues and environmental issues. In addition to higher power requirement, this prior art approach does not eliminate the coupling issue.
Another prior art approach is to reduce the effective (R-L-C) impedance of the signal lines and thereby increasing the spacing between signal lines. In general, increasing the spacing between signal lines by three-fold, the coupling effect will only be reduced by fifty percent. This prior art approach is usually combined with the first prior art approach to minimize coupling and reduce signal to noise ratio. This approach is inconsistent with modern trends for circuit compactness.
Yet another prior art approach is to shield the signal lines by using either a supply voltage like VDD or ground. Utilizing this prior art approach, the shielding line (ground) would need to be wide enough (with low impedance) so that the shield itself will not begin to transfer the noise to other signal lines.
These prior art approaches that tend to compensate by increasing signal strength combined with the prior art approach of providing a shielding line adjacent to signal line are shown in FIG. 1. As shown in this depiction, 100, the signal line 110 is routed along with the shielding line 120, which is then utilized to shield the noise from a neighboring signal line. For sub-micron technologies, the lengths of these signal and shield lines can become relatively long with respect to line thickness and thus can lead to high signal to noise ratio or cross-talk within a said circuit on a given substrate.
Therefore, a need exists for reducing the capacitive and inductive signal coupling effects of routing resources of an IC device.